Implement support for automatic generation of Table of Contents.

Implement support for automatic generation of Table of Contents.
It is triggered by <toc/> element.
Section header is not included into generation, so the complete code fragment to add will be
<section name="Table of Contents">
<toc/>
</section>
The html-manager-howto.xml provides a usage example for this.
Also corrected minor issues with tags nesting, reported by w3c validator.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@918073 13f79535-47bb-0310-9956-ffa450edef68